Zirconia toughened alumina esd safe ceramic composition, component, and methods for making same

ABSTRACT

ESD safe ceramic component is provided which includes a sintered composition which is formed of a base material and a resistivity modifier. The base material includes a primary component and a secondary component, the primary component including Al 2 O 3  and the secondary component including tetragonal-ZrO 2 .

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority to U.S. Provisional ApplicationNo. 60/428,402, filed Nov. 22, 2002 and is incorporated herein byreference.

BACKGROUND

1. Field of the Invention

The present invention is generally related to electrostatic discharge(ESD) safe ceramic (sometimes “ESD dissipative ceramic,” or “ESDceramic”) compositions, components, and methods for forming same, and inparticular is drawn to ESD safe ceramic components based upon a zirconiatoughened alumina (ZTA) material.

2. Description of the Related Art

In the area of electrostatic discharge (ESD) safe ceramics, variouscompositions have been developed in an attempt to bring togetherimportant electrical, thermal and mechanical properties of materials forend use applications that are sensitive to electrostatic discharge.

Most notably, zirconia-based materials have been investigated for use inenvironments sensitive to ESD. Generally speaking, zirconia istransformation-toughened, containing a stabilizer to partially stabilizethe zirconia in a tetragonal crystal structure. Among various toughenedzirconias, tetragonal partially stabilized zirconia has balancedproperties including high strength, fracture toughness, corrosionresistance, and excellent machinability. For these reasons, tetragonalpartially stabilized zirconia has been used for metal forming tools,blades/knifes, handling tools (e.g., tweezers), and optical fiberconnectors (ferrules), and have found recent use replacing tool steels,stainless steels, special alloys and cemented tungsten carbides (WC).

However, because toughened alumina is an electrical insulator having avolume resistivity greater than 10¹² Ohm-cm, it is not particularlysuitable for ESD safe applications. In this regard, a technicalbackground relating to the need for improved ESD materials can be foundby reviewing publicly available information from the ESD association.See www.esda.org., for example.

Recently, a need has arisen in the art for ESD dissipative or ESD safecomponents which not only have desirable ESD properties, but which alsohave desirable thermal expansion properties, flexural strength,toughness, hardness, wear resistance, and other properties. Some of thedemand is motivated by the need to find ESD safe materials which finduse in certain demanding commercial applications such as bonding tipsfor microelectronic use, handling tools for magneto-resistive headfabrication, bonding capillaries, and similar applications. In thisregard, zirconia based ceramics, including zirconia based ESD ceramicshave been found to lack sufficient rigidity, stiffness, wear resistance,and abrasion resistance for certain demanding tool applications. Inaddition, it has also been found that zirconia based ESD ceramics maynot have suitable thermal conductivity and thermal expansion properties.

Accordingly, based on the foregoing, the present inventors haverecognized a need in the art for improved materials finding particularuse in demanding applications, which require unique mechanical,structural and electrical properties.

SUMMARY

According to one aspect of the invention, an ESD safe ceramic componentincludes a sintered composition which is formed of a base material and aresistivity modifier. The base material includes a primary component anda secondary component, the primary component comprising Al₂O₃ and thesecondary component comprising tetragonal-ZrO₂.

According to another feature of the present invention, a method forforming an ESD safe ceramic component is provided in which a ceramicbody is densified at a relatively low temperature, such as less thanabout 1400° C. In this regard, the ceramic body is formed of a basematerial and a resistivity modifier, the base material including aprimary component comprised of Al₂O₃ and a secondary component comprisedof tetragonal-ZrO₂.

According to yet another feature of the present invention, a method forforming an ESD safe ceramic component is provided in which a basematerial and a resistivity modifier are mixed together, then formed intoa ceramic body, which is then sintered. In this regard, the basematerial, in line with the foregoing description, includes Al₂O₃ andtetragonal-ZrO₂. Of significance, according to one aspect of theinvention, the tetragonal-ZrO₂ contains a stabilizer which is presentand pre-alloyed with the tetragonal-ZrO₂ prior to mixing with theresistivity modifier, and of course, prior to forming the ceramic body.

According to another aspect of the present invention, a method forforming an ESD safe ceramic component is provided in which a ceramicbody is sintered including a base material and a resistivity modifier inline with the foregoing description, and thereafter, the resistivity isadjusted by an annealing operation.

According to another aspect of the present invention, an ESD safeceramic bonding tool is formed from a sintered composition comprising abase material and a resistivity modifier. The base material is formedfrom zirconia toughened alumina, and the resistivity modifier is formedof a transition metal oxide. The tool has a density not less than about98% of theoretical density and a volume resistivity within a range ofabout 10⁶ to about 10⁹ ohm/cm.

According to another aspect of the present invention, a method forforming a ceramic component is provided including hot isostatic pressing(HIPing) a ceramic body in a HIPing environment, the ceramic componentbeing provided in a localized environment containing a processing gasspecies having a partial pressure greater than the partial pressure ofthe processing gas species in the HIPing environment. That is, theprocessing gas species is generally rich in the localized environmentrelative to the entire HIPing environment in which HIPing is carriedout.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a bonding tool according to anembodiment of the present invention.

FIG. 2 shows a side view of the bonding tool, including an ultrasonicgenerator for effecting bonding operations.

FIG. 3 illustrates a configuration of a crucible structure in whichHIPing is carried out according to an embodiment of the presentinvention.

FIG. 4 illustrates an exploded cross-sectional view of the cruciblestructure shown in FIG. 3, additionally containing gettering materials.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The subject matter of copending U.S. patent application Ser. No.09/988,894, filed Nov. 19, 2001, commonly assigned to the presentassignee, is incorporated herein by reference.

According to one aspect of the present invention, an ESD safe ceramiccomponent is formed of a sintered composition which includes a basematerial and a resistivity modifier. In this regard, the base materialis formed of a zirconia toughened alumina (ZTA). The zirconia toughenedalumina includes a primary component of alumina (Al₂O₃) and a secondarycomponent comprising zirconia (ZrO₂). ZrO₂, in general, includes atleast three phases, including monoclinic, tetragonal, and cubic.Preferably, according to an embodiment of the present invention, thezirconia contains tetragonal zirconia, although monoclinic and cubicphases may be present. In this regard, in certain embodiments, a certainproportion of the monoclinic phase may be desirable for transformationtoughening properties.

Typically the zirconia contains at least 75 vol % tetragonal zirconia,such as at least 85 vol % tetragonal zirconia. Since the tetragonal formof zirconia is generally considered unstable or metastable at roomtemperature, typically a stabilizer is present within the crystalstructure, i.e., crystal lattice, of the zirconia material. Thestabilizer can be chosen from one of numerous materials, including rareearth oxides such as yttria, ceria and/or scandia. While the level ofthe stabilizer relative to the zirconia varies depending upon theparticular stabilizer utilized, typically the stabilizer is presentwithin a range of about 1 to about 8 mol %, and more typically within arange of about 2 mol % to about 4.5 mol % with respect to the zirconia.According to one embodiment, the zirconia is stabilized prior tointroduction with the resistivity modifier, and prior to formation ofthe ESD safe ceramic component. Introduction of the stabilizer orstabilizing agent at an early stage is generally referred to as“pre-alloying” the zirconia material. It may be desirable to executepre-alloying of the zirconia in order to prevent unwanted chemicalreactions during high temperature sintering operations. For example,such unwanted chemical reactions can cause undesirable changes in themechanical, thermal and electrical properties of the component such asby adversely changing the resistivity of the component through formationof undesirable phases.

Turning to the base material, according to one embodiment of the presentinvention, more alumina is present than zirconia. The ratio of aluminato zirconia may be greater than 55:45, based on volume percent, such asnot less than 60:40. Other embodiments include a higher proportion ofalumina relative to zirconia, such as on the order of not less than70:30, and 75:25.

Typically, the alumina in the form of the primary component of the basematerial forms a primary phase, sometimes understood in the art as amatrix phase of the base material. The secondary component, zirconia, inone embodiment is dispersed finely and evenly throughout the primaryphase. As noted above, the secondary phase is formed of tetragonalzirconia. However, additional phases, such as monoclinic and cubic formsof tetragonal may also be present.

Turning the resistivity modifier, a resistivity modifier is utilizedgenerally to decrease the volume and surface resistivity of thecomponent. Most typically, the resistivity modifier is present within arange of about 5 to 40 vol % with respect to the base material.Depending upon the particular resistivity modifier used, narrower rangesmay be also utilized, such as within a range of about 5 to about 30 vol%, or about 10 to 30 vol %. The resistivity modifier may increase ordecrease the resistivity, but is typically employed to reduce theresistivity, both volume resistivity and surface resistivity of thecomponent. In one form, the resistivity modifier takes on the form of aconductive particulate. Preferably, the modifier is not reactive withthe alumina and/or zirconia. For example, ZnO can form non-conductiveZnAl₂O₄ (zinc aluminate) due to reaction with the alumina base material,and therefore is not desirable. The following is a list of resistivitymodifiers which may be considered for use in connection with embodimentsof the present invention.

Carbides (B₄C, SiC, TiC, Cr₄C, VC, ZrC, TaC, WC, graphite, carbon);Nitrides (TiN, ZrN, HfN); Borides (TiB₂, ZrB₂, CaB₆, LaB₆, NbB₂);Silicides (MoSi₂,); Carbonitrides (Ti(C,N), Si(CN)); Single oxides (NiO,FeO, MnO, Co₂O₃, Cr₂O₃, Fe₂O₃, Ga₂O₃, In₂O₃, GeO₂, MnO₂, TiO_(2-x),RuO₂, Rh₂O₃, V₂O₃, Nb₂O₅, Ta₂O₅, WO₃); Doped oxides (SnO₂, CeO₂, TiO₂,ITO); Perovskites (MgTiO₃, CaTiO₃, BaTiO₃, SrTiO₃, LaCrO₃, LaFeO₃,LaMnO₃, YMnO₃, MgTiO₃F, FeTiO₃, SrSnO₃, CaSnO₃, LiNbO₃); Spinels (Fe₃O₄,MgFe₂O₄, MnFe₂O₄, CoFe₂O₄, NiFe₂O₄ ZnFe₂O₄, CoFe₂O₄, CoFe₂O₄, FeAl₂O₄,MnAl₂O₄, ZnAl₂O₄, ZnLa₂O₄, FeAl₂O₄, MgIn₂O₄, MnIn₂O₄, FeCr₂O₄, NiCr₂O₄,ZnGa₂O₄, LaTaO₄, NdTaO₄); Magnetoplumbite (BaFe₁₂O₁₉,); Garnet(3Y₂O₃*5Fe₂O₃); and Other oxides (Bi₂Ru₂O₇,)

Typically, the conductive particulate is chosen from a group consistingof oxides, carbides, nitrides, oxycarbides, oxynitrides, andoxycarbonitrides. Particularly suitable conductive particulates includetransition metal oxides (including compound oxides) such as TiO₂, MnO₂,Fe₂O₃, CoO, NiO, SiC, Cr₂O₃, SnO₂, ZrC, LaMnO₃, BaO 6Fe₂O₃, LaCrO₃, andSrCrO₃. Transition metal oxides such as Fe₂O₃, TiO₂ and MnO₂ areparticularly suitable for use in connection with embodiments herein.

In forming the ceramic component, typically, the base material is in theform of zirconia toughened alumina, or as separate powders of aluminaand zirconia which together form zirconia toughened alumina, are mixedwith a resistivity modifier as described above. Mixing may be carriedout by any one of conventional means, such as by mixing in an aqueous ororganic solution to form a slurry in a device such as a jar mill. As isunderstood in the art, dispersants and other additives may be utilized,although typically no sintering aids are utilized. In this case, laterstage sintering can be carried out by solid state diffusion, takingadvantage of the solid solubility of the materials. The slurry may beused directly to form certain types of bodies, such as by slip castingor the like. Alternatively, the slurry may be dried into granules forlater stage processing, such as shaping by pressing into a desiredshape. At this stage, the shaped bodies are typically understood to be“green” in the form of green compacts or green ceramic bodies.

According to a particular feature of an embodiment of the presentinvention, sintering to densify the ceramic body is carried out at arelatively low temperature. Low temperature sintering is particularlydesirable to prevent unwanted chemical reactions and formation ofundesirable phases in the ceramic body. According to one feature of thepresent invention, the green body is sintered at a temperature notgreater than about 1400° C., such as not greater than about 1350° C.

While sintering may be carried out under a pressureless sinteringoperation, such as under vacuum or atmospheric pressure in the presenceof ambient air, or inert gases, sintering may also be carried out by hotpressing or hot isostatic pressing (HIP). Further, a combination ofsintering operations may be utilized. According to one embodiment of thepresent invention, pressureless sintering is carried out to densify theceramic body and achieve a density of at least 95% of theoreticaldensity (T.D.). If needed by the final application of the component, thepart may be further densified by exposure to a HIP process, such as at atemperature within a range of 1100° C. to about 1400° C. HIPing may becarried out as is understood in the art by use of a fluid, such as a gasor liquid. In one embodiment, an inert gas such as argon may be utilizedto achieve a pressure above 100 MPa, such as on the order of 150-400MPa.

Further, optionally, the characteristics of the ESD safe ceramiccomponent may be fine-tuned by later stage processing. For example, theresistivity of the ESD safe ceramic component may be modified by a latestage process such as annealing. For example, components subjected topressureless sintering and HIPing may be then heat treated in air at atemperature within a range of about 600° C. to about 1200° C. for a timeperiod on the order of 0.5 to 100 hours, such as about 1 to about 5hours, to reach a desired resistivity such as in a range within about10⁵ to 10¹¹ Ohm-cm. According to certain embodiments, the volumeresistivity of the ESD safe ceramic component falls within a slightlynarrower range, such as within a range of about 106 to 10⁹ Ohm-cm.

According to embodiments of the present invention, desirable mechanicalproperties are achieved. For example, the ESD safe ceramic component mayhave a relatively high Young's Modulus, such as greater than about 230GPa, and even greater than about 240 GPa. The hardness of the componentmay also be fairly high which contributes relatively high wearresistance, which is desirable for certain applications. For example,the Vickers Hardness may be greater than about 13 GPa, such as greaterthan about 14 GPa.

According to one embodiment, the component has a fairly fine crystalstructure, namely having a grain size not greater than about 1 μm. It isnoted that certain embodiments have a multi-phase structure, such as,including three main phases: zirconia, alumina, and resistivitymodifier. The foregoing grain size is average grain size along arepresentative portion, including the main phases of the sample.

Further, according to certain embodiments of the present invention, thethermal expansion coefficient of the ESD safe ceramic component isrelatively well matched for its intended environment. For example, forcertain applications it is desirable for the thermal expansioncoefficient to fairly closely match that of AlTiC substrates. Inaddition, certain ESD safe ceramic component may have thermal expansioncoefficents that match well with commercially used tool steels andstainless steel, for example. Such thermal expansion matching may beeffective to help prevent warping due to thermal stress duringprocessing operations. In line with the foregoing, an embodiment of thepresent invention has a thermal expansion coefficient less than about10.0×10⁻⁶K⁻¹. Further, the thermal expansion coefficient may be lessthan about 9.5×10⁻⁶K⁻¹. According to one embodiment, the thermalexpansion coefficient is greater than about 8.0×10⁻⁶K⁻¹.

Further, according to another feature, the ESD safe ceramic componentmay have a relatively high density, such at least about 98% oftheoretical density. Other embodiments are even denser, having a minimumdensity of 99%, and even 99.5% of the theoretical density.

In addition to desirably density, thermal expansion, and mechanicalproperties, embodiments also demonstrate desirable magnetic properties,as well as color, which is particularly important for some processingoperations that rely on optical imaging components for process flow. Forexample, the certain embodiments have demonstrated a coercive magneticfield Hc not greater than about 5 E4 A/m, and component has a residualmagnetic induction Mr of not greater than 10 Gauss. As to opticalproperties, the embodiments have been measured to have an L* not lessthan about 35.

The final geometric configuration of the ESD safe ceramic component mayvary depending upon the intended use of the component. For example, thecomponent may take on a form of wire bonding tips, wire bondingcapillaries, magneto-resistive handling tools, substrates, carriers,slicing tools, dicing tools, de-gluing carrier tools, pick and placetools, semiconductor device packaging tools, single and two step probes,and test sockets. Embodiments of the present invention also call forusing these tools in their intended environments, such as executing awire bonding operation, handling MR heads, packaging IC devices and thelike.

EXAMPLE 1

AZ67 powder, a ZTA (zirconia toughened alumina) with 20 vol. % Y-TZP and80 vol. % Al₂O₃, available from Saint-Gobain Ceramics & Plastics inColorado Springs, Colo., is mixed with submicron Fe₂O₃ in ajar mill. Themill is charged with Y-TZP milling media, deionized water, anddispersant. The milling was performed for 10 hours in order to assure ahomogeneous mixing. The mixed slurry from the milling was dried using aRoto-Vap or spray dryer. It was found that a magnetic stirrer must beavoided in order to eliminate any segregation of slightly magneticparticles such as Fe₂O₃. The dried granules were pressed into disks orsquare tiles using steel molds followed by a CIPing (cold isostaticpressing) at 207 MPa (30,000 psi). These pressed parts of ˜55% relativedensity (“or green compacts”) were sintered at 1,200 to 1,400° C. for 1hour in air using a furnace with moly-disilicide (MoSi₂) heatingelements to achieve a sintered density of >95% T.D. (theoreticaldensity), as summarized in Table 1. The T.D. of each composition wasestimated by a rule of mixture assuming negligible reactions betweenphases. The density of sintered parts was measured by a waterdisplacement method. Some sintered parts were further densified byHIPing (hot isostatic pressing) at 1,200-1,350° C. and for 45 min inargon pressure of 207 MPa to achieve substantially pore-free parts. Theelectrical surface resistance of sintered or HIPed parts were measuredby the mean of a concentric probe per ESD S11.11. Some HIPed parts wereheat treated in air at 700-950 C for 1-5 hrs to a desired ESD surfaceresistance, 10⁵-10¹¹ Ohm.

The Young's modulus (E) of HIPed parts was measured by a pulse-echomethod to be ˜270 GPa compared to ˜200 GPa for Y-TZP based ESD safeceramics.

The hardness of dense material was measured by Vickers hardness methodusing an indentation load of 1-5 Kgf and showed between 13-15 GPacompared to 10-12 GPa for Y-TZP based ESD safe ceramics.

Surprisingly, it was found that the sintering of desired mixture couldbe performed at a significantly lower temperature (e.g., lower than1400° C., such as about 1,250° C.) than usual sintering temperatures.For instance, sintering temperatures of alumina, zirconia or ZTA aretypically on the order of 1500° C., and even higher. The low temperaturesintering is desirable for reduced reaction between dissimilar phases,reduced grain growth, and low densification cost. Further, it was foundthat a sintering at 1,400° C. or higher can result in a lower sintereddensity than at 1,250° C.

The results of resistivity measurements indicate that the desired ESDsafe ZTA based ceramics can be prepared mixing alumina into ESD safeY-TZP compositions.

EXAMPLE 2

AZ93 powder, a ZTA (zirconia toughened alumina) with 40 vol. % Y-TZP and60 vol. % Al₂O₃, available from Saint-Gobain Ceramics & Plastics inColorado Springs, Colo., is mixed with submicron Fe₂O₃ in ajar mill. Therest of processing method is same as Example 1. The results indicatethat the ESD safe ZTA based ceramics an also be prepared with AZ93powder. TABLE 1 Densification and Resistivities of ZTA based ESDdissipative ceramics before and after heat treatment Sintered HIPed HeatSurface Sintering Sintered surface HIPed HIPed surface TreatmentResistance ZTA Fe2O3 temp density resistance temp density resistance inair after HT type (vol %) (° C./Hr) (% TD) (Ohm) ¹ (° C.) (% TD) (Ohm) ¹(° C./Hr) (Ohm) ¹ 1 AZ67 18.6 1200/1 86* 2 AZ67 18.6 1250/1 99.6 1.52E111200 100 6.04E9 3 AZ67 23.3 1250/1 99 7.28E10 1200 100 3.45E7 4 AZ6723.3 1400/1 96 1.3E5 1350 96.5 2.51E4 700/2 6.94E4 5 AZ67 28.4 1250/1 991.77E6 1200 100 6.50E3 850/12 1.40E6 6 AZ67 28.4 1300/1 98 4.23E5 850/302.29E7 7 AZ93 21.25 1250/1 98.9 1.19E11 1200 99.7 1.80E10 8 AZ93 21.251400/1 97 9.3E4 1350 97.3 1.40E4 850/7 Cracked 9 AZ93 25 1250/1 992.13E7 1200 99.52 5.12E4 700/12 8.5E7 10 AZ93 23.3 1250/1 98.6 1.00E71200 99.98 1.70E5 11 AZ93 23.3 1250/1 97.6 6.4E7 1200 ² 99.95 5.00E6*open porosity¹ per BSD S11.11² HIP with oxygen generating powder bed

According to yet another aspect of the present invention, a method forforming ceramic components includes hot isostatic pressing (HIPing) aceramic body in a HIPing environment, the ceramic component beingprovided in a localized environment containing a processing gas specieshaving a partial pressure greater than a partial pressure of theprocessing gas species in the HIPing environment. While descriptionherein relates to ESD safe ceramics, and more particularly, to ZTA-basedESD safe ceramics, the foregoing method is particularly suitable forother ceramics, particularly those that benefit from a localizedenvironment during HIPing.

According to a particular feature, HIPing of certain ceramic componentsmay be advantageously carried out by utilizing a localized environment.In the context of ZTA-based ESD safe ceramics, it was found that certaingeometries might be subject to unwanted chemical reactions duringHIPing, even when utilizing an inert gas such as argon. In particular,additional testing beyond creation of relatively large scale workingsamples such as tiles was carried out on near-net shaped components thatwere of a generally fine scale, such as those demanded in themicroelectronic fabrication industry. One such example is the so-calledbonding tool notably including a wire-bonding tip and capillary.

The bonding tip may be advantageously formed from cylindrical rodshaving a generally fine structure, typically having a diameter on theorder of 2 mm nominally 1.6 mm. The rods may have a generally highaspect ratio, such as greater than about 3:1, 5:1 or even greater thanabout 10: 1. The aspect ratio is defined as the ratio of the length tothe next largest dimension of the component, and in the case cylindricalrods, the next largest dimension is the diameter. Such rods or rodstocks may be formed in a green state by an extrusion process orinjection molding. It was discovered that following HIPing in argon thatthe properties of the rods undesirably changed. In particular, the rodsemerged from HIPing having a darker color a lowered resistivity,typically on the order of 5×10⁴ ohm/cm (as contrasted with 5×10⁶ohm/cm), suggesting a thermochemical reduction of Fe₂O₃ (hematite) intoFe₂O₄ (magnetite), and FeO, and subsequent reaction with Al2O3. That is,the Fe₂O₃ resistivity modifier is reduced during HIPing. The samplesalso showed appreciably lower Vickers hardness indicting residualporosity after HIPing, as well as ferromagnetism.

Oftentimes, standard HIPing processes take place in an environment thathas a low oxygen partial pressure, such on the order of 10⁻¹² bar, whilethe HIPing environment is principally made up of non-reactive gases,such as inert or noble gases. A common gas is argon. One potentialapproach of addressing the problems associated with reduction ofresistivity modifiers such as transition metal oxides (as demonstratedby the reduction of Fe₂O₃), would be to oxygen-HIP the ceramiccomponents. However, oxygen-HIPing is not particularly cost effective,generally requiring the use of platinum lined thermal shields in an airor oxygen-containing atmosphere.

According to an embodiment, processing was carried out with a localizedprocessing gas, notably oxygen, the processing gas being generallyconfined to a specific volume within the HIPing environment generallysurrounding the ceramic components undergoing processing. This approachis effective to attenuate reduction of transition metal oxides,including Fe₂O₃, TiO₂ and MnO₂, which would otherwise reduce in theextremely low oxygen partial pressure associated with traditional HIPingprocesses. Attenuation of reduction of such oxides generally results inlowered residual porosity and damage such as bloating, cavity formation,and cracking. In addition, the electrical resistivity properties of thebefore-HIPed components are generally preserved post-HIPing.

As to the creation of the localized environment, various approaches maybe utilized. According to one approach, the components undergoing HIPingare provided in a crucible, a refractory container in which work piecesare set for thermal processing. The crucible can contain a processinggas source, and defines therein the localized environment. Theprocessing gas source is generally one that releases a desired gaseousspecies, creating a localized rich area. In the context of prevention ofreduction of resistivity modifiers such as transition metal oxides, anoxygen gas sources is provided. The oxygen gas source may be desirablyprovided in powder form, which has relatively high surface area furtherpromoting release of the desired processing gaseous species. In thisregard, the components undergoing HIPing may be placed on a powder bedor embedded within a powder bed formed of the gas source.

In the context of oxygen-releasing sources, it is preferable that theprocessing gas source undergoes reduction to establish a desirableoxygen partial pressure within the localized environment, before anyappreciable reduction of the ceramic component. The processing gassource generally undergoes reduction more easily than the resistivitymodifier. This ease of reduction is a function of the free energy changeof thermochemical reduction and oxidation as a function of temperatureand may be determined by thermodynamic data from the Ellingham diagramwhich is provided, for example, in R. A. Swalin, Thermodynamics ofSolids, 2^(nd) Edition, Wiley-Interscience Publications, pages 114(1972), hereby incorporated by reference. In a way, the powder acts as asacrificial HIPing agent undergoing reduction prior to any appreciablereduction of the ceramic component, thereby creating the desiredlocalized environment and protecting the ceramic component. Generally,the localized oxygen partial pressure is greater than the equilibriumoxygen partial pressure of the HIPing environment at a given temperatureand pressure of the system. Desirably, the partial pressure of oxygen isnot less than about 0. 1 atm in the localized environment and in someembodiments, not less than 0.5 atm. In contrast, the HIPing environmenthas a reduced partial pressure of oxygen, such as on the order of 10⁻¹⁰and lower.

In the context of providing a stable localized environment, applicantshave utilized various configurations of crucibles having a configurationthat minimizes gas flow therethrough during HIPing to stably contain thelocalized oxygen rich environment, and to prevent the processing gasspecies from appreciably escaping the crucible and contaminating theHIPing environment. In particular, it is generally desirable to providea crucible, which has only a single opening, to attenuate convectiveflow of gases therethrough. In addition, a gettering species may beprovided in the opening, or adjacent the opening to getter theprocessing gas species that would otherwise escape into the HIPingenvironment. For example, in the case of oxygen processing gas species,the getterer may be a metal that oxidizes in the high temperature HIPingenvironment upon contact with the oxygen from the gas source.

The following examples illustrate various working embodiments of variouscomponents, notably including the formation of ceramic components byHIPing having a localized environment.

EXAMPLE 3

A ZTA (AZ93 available from Saint-Gobain Ceramics & Plastics in ColoradoSprings, Colo., 40 vol % Y-TZP, 60 vol % Al₂O₃) was mixed with milledFe₂O₃ powder (milled to a specific surface area of 13 m²/g, Alpha Aesarof Ward Hill, Mass.) in water by milling with zirconia (Y-TZP) millingmedia, followed by spray drying. The spray-dried powder was pressed intorectangular tiles using a steel mold followed by CIPing at 207 MPa to agreen density ˜55% T.D.

The CIPed tiles was sintered at 1250° C. for 1 hr in air to a sintereddensity of ˜98% T.D. The color of sintered tiles was red. The tiles werenot attracted to a permanent magnet. The resistivity of material by theDC resistivity measurement was ˜5×10⁷ Ω-cm, which is good for the ESDdissipation.

Sintered samples were HIPed in nested alumina crucibles filled withzirconia (Y-TZP) bubbles and with an oxygen-generating oxide powder(Pr₆O₁₁, MnO₂, or CoO) bed on bottom. Some samples were HIPed withoutthe oxygen-generating powder. The HIPing was performed at 1200° C. inargon pressure of 207 MPa with graphite heating elements.

A few oxygen-generating powders were used and found effective. Forinstance, Pr₆O₁₁, MnO₂, and CoO powders are thermochemically reducedmore easily compared to Fe₂O₃, and thus are effective to prevent orattenuate the reduction of Fe₂O₃ into Fe₃O₄. Generally speaking, theoxygen-generating powders are chosen from those that undergo reductionbefore reduction of the resistivity modifier during processing.

Most samples HIPed with the oxygen-generating powders showed the samecolor after the HIPing with the density mostly higher than 99.8%, andshowed resistivities similar to those of sintered values, 5×10⁶-10⁸Ω-cm. On the other hand, samples HIPed without oxygen-generating powderbed were much darker in their color, often close to black, showed alower density of <99.8% T.D., and resistivities significantly lower thansintered values, for instance ˜5×10²-10⁴ Ω-cm.

The HIPed samples showed a high Young's modulus of 270 GPa and highhardness of 15.3 GPa at 1 kgf load of Vickers indentation. The materialis significantly stiffer and harder compared to values of Y-TZP basedESD safe ceramics: 200 GPa and 10 GPa, respectively. Therefore theabrasive wear resistance of this material should be significantly betterthan the Y-TZP based ESD safe ceramics.

EXAMPLE 4

The same material in Example 3 was formed into thin rods of 2 mmdiameter by the hot wax extrusion. First, the mixture of AZ93 and Fe₂O₃powder was further mixed with wax at high temperature. The extruded rodswere sintered in air at 1275° C. to ˜97% T.D. The sintered rods werefurther HIPed with oxygen-generating powder bed at 1250° C. and 207 MPaof argon. The HIPed rods were red in color, non-magnetic, and highdensity of >99.8% T.D. The resistivity of HIPed rods remainedapproximately same as sintered rods to 5×10⁷ Ω-cm.

EXAMPLE 5

The HIPed rods of Example 4 were machined into wire bonding tips. Thematerial has a significantly higher Young's modulus of 270 GPa andVickers hardness of 15.3 GPa at indentation load of 1 kgf compared toY-TZP based ESD safe ceramics. The material is advantageous for aneffective ultrasonic bonding and improved wear resistance.

EXAMPLE 6

The oxygen generating powder is reduced during the HIPing. In particularthe used Pr₆O₁₁ shows a lighter color after oxygen depletion. The usedpowder can be heat treated in air at 800-1,000° C. for 5 hr to reoxidizeit back to Pr₆O₁₁. Therefore, the oxygen-generating powder can be easilyregenerated for repeated use in processing additional ESD safecomponents.

EXAMPLE 7

Silicon carbide (SiC) crucible is often more durable for industrialapplications with good hot strength and thermal conductivity. A SiCcrucible available from Saint-Gobain Industrial Ceramics of Worcester,Mass., was used in a HIPing by the same method as Example 1. AfterHIPing it was found that the HIPed samples were dark, rather magnetic,and showed a lower resistivity. The crucible was passivated by heatingin air at 1,000° C. for 5 hr to form an oxide layer. The same cycle wasrepeated with the passivated crucible. The HIPed samples from thepassivated crucibles were then found to have essentially the sameproperties as samples processed using alumina crucibles. It is suspectedthat the oxygen may be consumed in the virgin SiC crucible during theHIPing creating a reducing environment.

EXAMPLE 8

A ZTA (AZ93 available from Saint-Gobain Ceramics & Plastics in ColoradoSprings, Colo.) was mixed with milled Fe₂O₃ powder (milled to a specificsurface area of 13 m²/g, Alpha Asaer) in water by milling with zirconia(Y-TZP) milling media, followed by spray drying. The spray-dried powderwas pressed into rectangular tiles using a steel mold followed by CIPingat 207 MPa to a green density ˜55% T.D.

The CIPed tiles was sintered at 1250° C. for 1 hr in air to a sintereddensity of ˜98% T.D. The color of sintered tiles was red. The tiles werenot attracted to a permanent magnet. The resistivity of material by theDC resistivity measurement was ˜5×10⁷ Ω-cm, which is good for the ESDdissipation.

Sintered samples were HIPed in alumina crucibles filled with zirconiabubbles. The HIPing was performed at 1200° C. in argon pressure of 207MPa with graphite heating elements.

The HIPed tiles were machined into MOR bars for 4-point bending testaccording to ASTM C1161-02b resulting in an average strength of 877 MPawith the maximum strength of 1,023 MPa. The fracture toughness wasmeasured by the indentation strength method to have superior values thanthose of alumina. The measured strength is significantly higher thanthose by sintering only (without pressure). Therefore, it is expectedthe HIPed material is advantageous for the grinding of complex shapesand low particle generation with an extended use.

The present results, particularly in connection with Examples 3-7,indicate that ceramics with thermochemically reducing compositions canbe HIPed in a reducing atmosphere in a crucible having an oxygen-richenvironment, such as an oxygen-generating feature such as a powder bed.The use of present HIPing technique is not limited to ESD safe ceramicshaving transition metal oxides as a resistivity modifier. For instance,a number of ceramics such as ferrites, varistors (including metal oxidevaristors (MOVs)), CeO₂, TiO₂, Ce-TZP, PZT (PbO—ZrO2-TiO3), PMN(PbO—MnO—NbO3), PLZT, BaTiO₃, SrTiO₃, etc. can be safely HIPed fordesired electromagnetic properties along with improved mechanicalreliability.

Further, some ceramics are difficult to sinter due to higher vaporpressure in non-oxidative atmosphere. Such ceramics can be HIPed to neartheoretical density by the foregoing HIPing process.

EXAMPLE 9

A ZTA (AZ93 available from Saint-Gobain Ceramics & Plastics in ColoradoSprings, Colo., 40 vol % Y-TZP, 60 vol % Al₂O₃) was mixed with milledFe₂O₃ powder (milled to a specific surface area of 13 m²/g, Alpha Aesarof Ward Hill, Mass.) in water by milling with zirconia (Y-TZP) millingmedia, followed by spray drying. The spray dried powder was then used ina hot wax extrusion process to produce thin rods of 2 mm in diameter.

Then with heating cycles the wax was burned out and the rods aresintered in air at 1325C for 1 hr to a density ˜97% TD. The sinteredrods were further HIPed with oxygen-generating powder bed at 1200° C.and 207 MPa of argon. The HIPed rods were red in color, non-magnetic,and high density of >99.8% T.D. The resistivity of HIPed rods remainedapproximately same as sintered rods to 5x10⁷ Ω-cm.

The rods 1.6 mm in diameter and 25 mm were heat treated in an aluminatube furnace at 600 C for 1 hr with a partial pressure of oxygen lessthan 100 ppm to a final resistivity of 2E5 Ohm.cm.

It has been shown that P0₂ can be used as control of the resistivityother than the soak temperature. A resistivity of 1.5E5 Ohm-cm isobtained with a heat treatment at 1000 C for 60 minutes under a pressureof PO2 ˜900 PPM

EXAMPLE 10

The resistivity of the material can be adjusted by how many chargecarriers are frozen from the high temperature heat treatment. This iscontrolled by soak time and cooling rate. For example surface resistanceof ZTA/Fe₂O₃ composition sintered in air can vary from 1E9 to 5E7 Ohm-cmby varying the cooling rate from 0.5 C/min to 10 C/min from thesintering temperature 1250 C to the room temperature.

As a further variant, the same material can be heat treated atresistivity as low as 7E3 Ohm.cm at 1000 C for 1 hr at a PO₂ lower than100 ppm for application requiring high conductivity such as ionizer tipfor air ionizer system. Higher temperature and lower PO₂ transform theFe₂O₃ phase into the Fe3O4 phase leading to even lower resistivity >5E3Ohm.cm but with residual magnetic properties and the part would turnblack in color.

EXAMPLE 11

A ZTA (AZ93 available from Saint-Gobain Ceramics & Plastics in ColoradoSprings, Colo., 40 vol % Y-TZP, 60 vol % Al₂O₃) was mixed with milledFe₂O₃ powder (milled to a specific surface area of 13 m²/g, Alpha Aesarof Ward Hill, Mass.) in water by milling with zirconia (Y-TZP) millingmedia, followed by spray drying. The spray dried powder was then used ina hot wax extrusion process to produce thin rods of 2 mm in diameter.

Then, with heating cycles the wax was burned out and the rods weresintered in air at 1325C for 1 hr to a density ˜97% TD. The sinteredrods were further HIPed with oxygen-generating powder bed at 1250° C.and 207 MPa of argon. The HIPed rods were red in color, non-magnetic,and high density of >99.8% T.D. The resistivity of HIPed rods remainedapproximately the same as sintered rods to 5×10⁷ Ω-cm.

EXAMPLE 12

A ZTA (AZ93 available from Saint-Gobain Ceramics & Plastics in ColoradoSprings, Colo., 40 vol % Y-TZP, 60 vol % Al₂O₃) was mixed with milledFe₂O₃ powder (milled to a specific surface area of 13 m²/g, Alpha Aesarof Ward Hill, Mass.) in water by milling with zirconia (Y-TZP) millingmedia, followed by spray drying. The spray-dried powder was pressed intoround pellets using a steel mold followed by CIPing at 207 MPa to agreen density ˜55% T.D.

The CIPed samples were sintered at 1250° C. for 1 hr in air to asintered density of ˜98% T.D.

The sintered samples were further HIPed with oxygen-generating powderbed at 1250° C. and 207 MPa of argon. The HIPed rods were red in color(non-black), non-magnetic, and high density of >99.8% T.D.

2 samples of 2 different batches of powders were prepared. Sample 1showed a volume resistivity measured by the DC 2 point technique of6.2E7 Ohm. cm. Sample 2 showed a volume resistivity measured by the DC 2points technique of 1.2E8 Ohm. cm.

Color was measured with a MiniScan XE plus from Hunter lab in the L*a*b*system. Sample Color L* Magnetism 1 Sintered red 40 No in air 2 Hippedwith brown 38 No powder bed 3 2 + heat red 41 No treatment in air 4Hipped without black 31 Yes powder bed

EXAMPLE 13

A ZTA (AZ93 available from Saint-Gobain Ceramics & Plastics in ColoradoSprings, Colo., 40 vol % Y-TZP, 60 vol % Al₂O₃) was mixed with milledFe₂O₃ powder (milled to a specific surface area of 13 m²/g, Alpha Aesarof Ward Hill, Mass.) in water by milling with zirconia (Y-TZP) millingmedia, followed by spray drying. The spray-dried powder was pressed intoround pellets using a steel mold followed by CIPing at 207 MPa to agreen density ˜55% T.D.

The CIPed samples were sintered at 1250° C. for 1 hr in air to asintered density of ˜98% T.D.

The sintered samples were further HIPed with an oxygen-generating powderbed at 1250° C. and 207 MPa of argon. The HIPed rods were red in color,non-magnetic, and high density of >99.8% T.D. The resistivity ofmaterial by the DC resistivity measurement was ˜5×10⁷ Ω-cm, which isgood for the ESD dissipation.

A magnetic hysteresis curve was measured with a vibrating magnetometer:residual magnetic induction (Mr) of 5.8 Gauss, a coercive magnetic field(Hc) of 3.7 E4 A/m, and a maximum induction of 31.7 Gauss at a magneticfield of 9.5 E5 A/m.

EXAMPLE 14

A ZTA (AZ93 available from Saint-Gobain Ceramics & Plastics in ColoradoSprings, Colo., 40 vol % Y-TZP, 60 vol % Al₂O₃) was mixed with milledFe₂O₃ powder (milled to a specific surface area of 13 m²/g, Alpha Aesarof Ward Hill, Mass.) in water by milling with zirconia (Y-TZP) millingmedia, followed by spray drying. The spray dried powder was then used ina hot wax extrusion process to produce thin rods of 2 mm in diameter.

Then, with heating cycles the wax is burned out and the rods aresintered in air at 1325 C for 1 hr to a density ˜97% TD. The sinteredrods were further HIPed with oxygen-generating powder bed at 1250° C.and 207 MPa of argon. The HIPed rods were red in color, non-magnetic,and high density of >99.8% T.D. The resistivity of HIPed rods remainedapproximately same as sintered rods to 5×10⁷ Ω-cm.

Then, rods 1.6 mm in diameter and 25 mm long were heat treated in analumina tube under various temperatures and partial pressures of oxygen.This heat treatment permitted adjustment of the volume resistivitywithin a range from E4 to E8 Ohm.cm.

To measure the capacity of this material to softly dissipate staticcharges, the rods were in contact on one side with a 20 pf aluminumplate charged at 1000V (Ion Systems Charged Plate Monitor Model 210 CPM)and ground by a metal contact (brass) on the other side. The platevoltage decrease was measured over time with a high frequencyoscilloscope at 25 MHz (LeCroy 9310AM Dual 400 MHz Oscilloscope). Thedecay time was taken as the time for the voltage of the plate todecrease from 900 V to 100 V. Volume resistivity Sample (Ohm · cm) Decaytime (ms) 2 10E4 20.7 3 10E5 20.8 4 10E6 39.6 5 10E7 110.0

The foregoing results are desirable, falling with target decay timebetween 10 and 500 ms. According to one feature, the ESD safe component,such as in the form of a bonding tool has a ESD safe characteristic suchthat a 1000V on the device with which it is in contact (such as amicroelectronic device undergoing bonding operations) is dissipated toabout 100 V in less than 500 ms.

Turning to the drawings, various embodiments are illustrated. As shownin FIGS. 1 and 2, a bonding tool 1 having a bonding tip 10 is formed ofZTA-based ESD safe ceramic materials as described herein. The bondingtip 10 having a generally cylindrical base portion and a conical tipportion is formed from sintered and HIPed rod stock having desirable ESDsafe properties. The bonding tip 10 may be formed of a monolithicceramic-based composition as described herein. The working end 14 istextured for gripping a work piece and for superior transfer ofultrasonic energy to the work piece for better bonding. Typically, theworkpiece is a wire that is to be bonded to a contact pad in amicroelectronic device. The bonding tool is used in a known manner andgenerally includes an ultrasonic source 16 coupled thereto forgenerating ultrasonic vibrations. In use, the working end 14 is placedin contact with and biased against the work piece, and the ultrasonicgenerator is engaged so as to impart the vibrations onto the work piece.By mechanical agitation via the ultrasonic waves and optionally with aidof thermal treatment, bonding of the work piece is carried out. In thecase of wire bonding, the wire is deformed mechanically and thermally soas to bond to an underlying contact pad.

FIG. 3 illustrates a simple crucible structure for creation of alocalized environment during HIPing as already described in detailabove. Here, nested crucibles 30 and 32 are configured such thatcrucible 32 is inverted and placed over crucible 30. A singular annularopening is provided between the two crucibles around the bottomperiphery of crucible 30. Here, crucible 30 contains ceramic components34 embedded within processing gas source in the form of a powder bed.

FIG. 4 illustrates a variation on the crucible structure. Getteringagent 40 is provided between the crucibles, through which the processinggas would escape into the HIPing environment. The guttering agent is asdescribed above, and generally attenuates the escape of the processinggas into the HIPing environment. Here, the gettering agent 40 is a metalpowder.

The above-disclosed subject matter is to be considered illustrative, andnot restrictive and the appended claims are intended to cover all suchmodifications, enhancements, equivalents, and other embodiments thatfall within the scope of the present invention. Thus, to the maximumextent allowed by law, the scope of the present invention is to bedetermined by the broadest permissible interpretation of the followingclaims and their equivalents and shall not be restricted or limited bythe foregoing detailed description.

1-35. (canceled)
 36. A method of forming an ESD safe ceramic component,comprising: densifying a ceramic body by heat treating, the ceramic bodycomprising (i) a base material of a zirconia toughened alumina, the basematerial comprising a primary component of Al₂O₃ and a secondarycomponent of ZrO₂, wherein the ZrO₂ comprises tetragonal ZrO₂, and (ii)a resistivity modifier to reduce an electrical resistivity of the basematerial, wherein heat treating is carried out at a temperature lessthan about 1400° C.
 37. The method of claim 36, wherein the heattreating is carried out by a method selected from pressureless sinteringpressure sintering, or a combination thereof.
 38. The method of claim37, wherein heat treating includes pressure sintering, pressuresintering being carried out by hot isostatic pressing (HIPing).
 39. Themethod of claim 36, wherein the temperature is not greater than about1350° C.
 40. A method of forming an ESD safe ceramic component,comprising: mixing together a base material and a resistivity modifier,the base material comprising Al₂O₃ and ZrO₂, wherein the ZrO₂ comprisespartially stabilized tetragonal ZrO₂ and contains a stabilizer such thatthe ZrO₂ is pre-alloyed; forming a ceramic body comprising the mixtureof the base material and the resistivity modifier, the ZrO₂ containingthe stabilizer prior to forming the ceramic body; and sintering theceramic body.
 41. A method of forming an ESD safe ceramic component,comprising: sintering a ceramic body comprising (i) a base material of azirconia toughened alumina, the base material comprising a primary phaseof Al₂O₃ and a secondary phase of ZrO₂, wherein the ZrO₂ comprisestetragonal ZrO₂, and (ii) a resistivity modifier to reduce an electricalresistivity of the base material, to form a densified body; andadjusting a resistivity of the densified body by annealing.
 42. Themethod of claim 41, wherein annealing is carried out in an oxygencontaining environment or in an inert gas environment.
 43. The method ofclaim 41, wherein annealing is carried out at a temperature within arange of about 600° C. to about 1200° C.
 44. A method of forming aceramic component, comprising: hot isostatic pressing (HIPing) a ceramicbody in a HIPing environment, the ceramic component being provided in alocalized environment containing a processing gas species having apartial pressure greater than the processing gas species in the HIPingenvironment.
 45. The method of claim 44, wherein the HIPing environmentcontains a noble gas, and the localized environment comprises oxygen,wherein the localized environment is oxygen-rich relative to the HIPingenvironment.
 46. The method of claim 44, wherein component is providedin a crucible containing processing gas source, the crucible defining avolume that is the localized environment.
 47. The method of claim 46,wherein the crucible is configured to attenuate gas flow therethrough.48. The method of claim 47, wherein the crucible has a single openingduring HIPing.
 49. The method of claim 46, wherein the processing gassource comprises a powder.
 50. The method of claim 49, wherein thecomponent is embedded in the powder.
 51. The method of claim 44, whereinthe ceramic component is an ESD safe ceramic component comprising a basematerial and a resistivity modifier to reduce an electrical resistivityof the base material.
 52. The method of claim 44, wherein the ceramiccomponent is comprised of at least one material from the groupconsisting of ferrites, varistors, CeO₂, TiO₂, Ce-TZP, PZT(PbO—ZrO2—TiO3), PMN (PbO—MnO—NbO3), PLZT, BaTiO₃, SrTiO₃.
 53. Themethod of claim 51, wherein the component is provided in a crucibleduring HIPing, the crucible containing processing gas source.
 54. Themethod of claim 53, wherein the processing gas source comprises amaterial that is more easily reduced than the resistivity modifier. 55.The method of claim 44, wherein material of a zirconia toughenedalumina, comprising a primary component of Al₂O₃ and a secondarycomponent of ZrO₂, wherein the ZrO₂ is comprised mostly of tetragonalZrO₂.
 56. The method of claim 44, wherein the processing gas species hasa partial pressure that is not less than about 0.1 atm in the localizedenvironment.
 57. The method of claim 44, wherein the processing gasspecies has a partial pressure that is not less than about 0.5 atm inthe localized environment.
 58. The method of claim 44, wherein theprocessing gas species is oxygen, the localized environment having agreater than an equilibrium oxygen partial pressure of the HIPingenvironment.
 59. The method of claim 44, wherein the ceramic componentis a rod.
 60. The method of claim 44, wherein the rod has an aspectratio greater than about 5:1.
 61. A method of bonding a microelectronicdevice, comprising: contacting the device with a bonding tool formed ofa sintered composition comprising (i) a base material of a zirconiatoughened alumina that comprises a primary component of Al₂O₃ and asecondary component of ZrO₂, wherein the ZrO₂ comprises tetragonal ZrO₂,and (ii) a resistivity modifier to reduce an electrical resistivity ofthe base material, the resistivity modifier comprising a transitionmetal oxide; and biasing the tool to effect bonding of themicroelectronic device.
 62. The method of claim 61, wherein biasing iscarried out by vibrating using ultrasonic waves.
 63. The method of claim61, wherein the microelectronic device includes a wire to be bonded to acontact, the bonding being carried out to bond the wire to the contact.64. The method of claim 61, wherein the bonding tool has a ESDcharacteristic such that a 1000V on the device is dissipated in lessthan 500 ms to about 100 V.